This invention relates to a process for the preparation of sodium methallyl sulfonate (MAS) from technical methallyl chloride (MAC) containing isocrotyl chloride (ICC) by a two-step reaction with aqueous sodium sulfite solution in an emulsion at temperatures of between 30.degree. and 80.degree. C.
Sodium methallyl sulfonate is an important monomer for copolymerization with other unsaturated monomers, particularly with acrylonitrile.
Commercial production of sodium methallyl sulfonate is carried out by reacting methallyl chloride with an aqueous solution of sodium sulfite at temperatures of 30.degree.-70.degree. C. The following equation represents the reaction: ##STR1##
This reaction is generally done using an excess of methallyl chloride. Conversion to the sulfonate reaches as high as about 99.3%, when pure methallyl chloride is used (Russian Pat. No. 438,647).
Methallyl chloride is customarily made by the chlorination of isobutene and MAC is obtained as a mixture containing considerable amounts of isomeric isocrotyl chloride (ICC) and more highly chlorinated by-products. Although more highly chlorinated by-products can be separated relatively easily by fractional distillation, separation of ICC from MAC by further fractionation is very expensive and pure MAC is expensive. In commercial procedures, isomeric mixtures of about 80-95% by weight of MAC and 5-20% by weight of ICC are obtained without excessive expenditures. Use of technical MAC/ICC mixtures for MAS production would therefore be advantageous, owing to the low cost of the mixture.
Reaction of MAC, in a mixture containing ICC, with Na.sub.2 SO.sub.3 is retarded by the presence of ICC, which does not react. When a technical mixture of 90% MAC and 10% ICC with a 1-2% excess of MAC with respect to Na.sub.2 SO.sub.3 is used, reaction time is prolonged approximately four-fold, compared to the reaction time of pure MAC. Retardation of the reaction can essentially be prevented by using a larger excess of MAC, for example, a 20% excess. However, when a 20% excess of MAC is used, mixtures of 60% MAC and 40% ICC are obtained after the reaction. This product is unsuitable for conventional methods of making MAS because the reaction rate is retarded by ICC. Attempted separation of the mixture by distillation to attain enrichment with respect to MAC is very expensive, because the separation is difficult and there is a considerable loss in yield of MAC. Consequently, use of technical MAC in conventional processes becomes increasingly less economical as the ICC content of the technical MAC/ICC mixture increases. The ICC in the reaction mixture is also unusable, because separating this mixture by distillation to enrich ICC content is also uneconomical.
Thus, there is a continuing need for developing an economical process for preparing MAS from technical MAC/ICC mixtures and sodium sulfite, with high conversions of MAC and Na.sub.2 SO.sub.3 and short reaction times.